A compulsive subway and bus thief was trying to take a new Long Island Rail Road locomotive and train

out of a Queens rail yard when he was busted after posing as a safety consultant, a prosecutor said yesterday.

Darius McCollum, 39, also admitted having stolen keys used to operate various train engines, including the

M-7 Bombardier locomotive he had been asking about Friday at the yard, said Queens District Attorney Richard Brown.

McCollum, who has 20 arrests for transit-related stunts, entered the train yards in Jamaica wearing an LIRR vest and hard hat, carrying publications from the commuter line’s parent Metropolitan Transportation Authority, and a phony business card, Brown said.

The card identified him as a “captain” and an “independent safety consultant.”

He has never held either title or any transit job. But the Lower East Side resident, who friends say has a mental disorder causing his obsessive behavior, has stolen several trains and buses over 23 years, including an E train that he commandeered for six stops at age 15 in 1981.

On Friday, McCollum presented his fake card to Bombardier representatives and asked them how to operate the new M-7 locomotives, which had been delivered to the LIRR and were in the yard, the DA said.

When his ID was called into question, he walked off, but was caught by MTA cops, who found the train keys on him.

McCollum, who had been free on parole for about two months when he arrested, is being held on $250,000 bail. He has been charged with attempted grand larceny, criminal impersonation and other charges in the case, which has raised questions about the efficacy of MTA security upgrades made after the 9/11 terror attacks.

Also yesterday, a source claimed McCollum began appearing at the Delancey and Essex streets subway

station near his home two weeks ago posing as a security consultant – complete with business cards like the

one he had in Queens.

Since then, he assisted workers who are upgrading the station with questions about Transit Authority

safety rules, said the source, adding that, “He knew his s- – -.”

McCollum’s past felony convictions could earn him life in prison if he is convicted of the new charges,

said Stephen Jackson, a lawyer who represented him when he was sentenced to prison in 2001 for entering a

subway control tower.

Jackson said that if he is hired again, he will argue that McCollum’s Asperger’s syndrome – an autism-like disorder characterized by obsessions with a topic – “seriously hinders his ability to distinguish right from